As known and summarizing, an ORC plant comprises at least a supply pump, at least a heat exchanger (usually, one or more evaporators but also one or more pre-heaters and one or more super-heaters), an expansion turbine, a condenser and eventually a regenerator. The performed thermodynamic cycle, organic Rankine cycle, is characterized in that the working fluid is an organic fluid. The cycle consists of two substantially adiabatic curves and two isobar curves with phase changes, to provide heat (evaporator) and subtract heat (condenser). The pump pressurizes the condensed liquid and feeds it to the evaporator, while the turbine transforms thermal energy into mechanical work. Therefore, aim of such a thermodynamic cycle is to transform, as much as possible, heat into mechanical work. The organic Rankine cycle is typically used in thermo-electric plants, to produce electrical energy.
In typical applications, rotational speeds and pressures usually require to adopt rotatable mechanical seals having an oil barrier to seal the working fluid from the external environment. The contact area between components, having a relative motion each other, requires a constant and pressurized lubrication, to ensure a perfect function and a long lifetime. In fact, such a lubrication reduces the wear, due to the direct contact between the two components. In such plants, an oil case is available for feeding all seals with pressurized oil. Said oil case must have a remarkable volume, typically 100-300 l for each megawatt of electric power, to provide lubrication for sealing and bearings of the turbines.
Typically, rotatable seals are susceptible to small oil losses. In some cases, also heavier losses can arise, due to a mechanical breakage of the sealing, as a consequence of technical inconveniences, for example thermal or mechanical overloads.
Typical small losses in an ORC plant are about 0.1÷0.5 l a day. Being at a greater pressure than the process operating pressure, the oil also flows inside the piping of the ORC plant and is mixed with the working fluid, thus changing physical and chemical characteristics of the working fluid. For example, due to such a mixing, the vapor tension of the organic fluid changes and, consequently, also its condensation pressure. Moreover, the chemical composition of the working fluid changes as well as the total flow-rate (which is the sum of working fluid and oil flow-rates). Such changes influence the thermal coefficient and the pressure of the performed cycle, worsening the global efficiency.
Therefore, a need exists for separating and removing the oil from the working fluid inside the plant, so as to grant a good efficiency along the lifetime.
At the time being, devices properly devoted for removing lubricating oil from sealing means as well as other high-boiling fluids (for example, thermal carrier fluids or component machining residual fluids) from the working fluid of an ORC plant are unknown.